In the domestic alcoholic fermentation industry, yeast alone or yeast in combination with acid protease is often used to produce alcohol, with the maximum final alcohol content in the mash being 11-12 v/v %. If the final alcohol content in the mash is further increased, the content of residual reducing sugar and starch in the mash would be relatively high, resulting in the decrease of alcohol yield for the raw material and the occurrence of pollution to the environment due to wasted residual reducing sugar, residual starch and alcoholic mash. Therefore, it has become a significant problem in urgent need of settling to increase the final alcohol content in the mash while keeping the contents of residual reducing sugar and residual starch at a relatively reasonable level.
As disclosed in the application “a composite yeast suitable for high concentration alcohol fermentation”, filed on Dec. 15, 2003 by the present applicant, a composite yeast comprising thermostable Saccharomyces cerevisiae, acid protease, phytase and cellulase is used as a ferment for alcohol fermentation, which may result in the mash of standard raw material such as corn, cassava, and wheat with a final alcohol content of 14.5-15.5 v/v %, with the residual reducing sugar content being controlled at 0.2-0.4 w/v % and the residual starch content being controlled at 1.0-2.0 w/v %.